Phenanthroline-Derivative Functionalized Carbon Dots for Highly Selective and Sensitive Detection of Cu2+ and S2− and Imaging inside Live Cells

Developing effective methods for the instant detection of Cu2+ and S2− is highly desired in the biological and environmental fields. Herein, a novel fluorescent nanoprobe was elaborately designed and synthesized by grafting a phenanthroline derivative onto the surface of carbon dots (CDs). The obtained functionalized CDs (FCDs) exhibited blue fluorescence (FL) with excellent photostability and possessed a mean diameter around 4 nm. Cu2+ can be selectively captured by the phenanthroline group of FCDs to generate an absorptive complex in situ, leading to obvious quenching of the FCDs’ FL signal through an inner filter effect. Furthermore, the FL of the FCD–Cu2+ can be effectively recovered by S2− anions due to the release of FCDs from the FCD–Cu2+ complex owing to the formation of stable CuS (Ksp = 1.27 × 10−36) between S2− and Cu2+. The detection limits of the FCDs were determined to be 40.1 nM and 88.9 nM for Cu2+ and S2−, respectively. Moreover, this nanoprobe can also be used for the imaging of intracellular Cu2+ and S2−, which shows strong application prospects in the field of biology.